Generally, fluids such as high-purity chemical products for semiconductors or general-use chemical products are filled into fluid tanks such as polyethylene tanks at a production facility, and they are shipped after a lid has been attached to a fluid port for filling and discharging that is formed in this fluid tank. As a method for removing the fluid that has been stored in such a fluid tank, a siphon hose method is known in which a gas such as air is introduced into the container, and the fluid is fed to the outside of the container due to the gas pressure that is produced thereby.
In this method, after removing the lid that was attached to the fluid port of the fluid tank, a plug is installed in the fluid port, and then a socket is connected in the plug. The plug is provided with a siphon hose, which forms a fluid path, and a gas supply duct. The socket is provided with a tube for removing fluid to the outside of the fluid tank and a tube for introducing gas. The socket enables the respective communication between its tube for removing fluid and the tube for introducing gas with the siphon hose and the gas supply duct of the plug. By connecting the socket into the plug, a fluid path for removing fluid and a gas path for introducing gas are formed. Such a fluid tank connector is disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. 2002-59993.
However, the above patent document discloses a plug that is fastened by being threaded onto an internal thread that has been formed on the inner periphery of the fluid port of the fluid tank. Therefore, the plug cannot be used in a container in which an external thread has been formed on the fluid port, that is, a container in which the thread for the installation of a cap that closes the fluid port is an external thread.
Thus, in order to connect the plug and the socket to a fluid tank in which the fluid port has an external thread, a construction can be considered in which the plug is disposed at the inner periphery of the fluid port, and a sleeve that is provided on the socket is then threaded onto the external thread of the fluid port. In this case, an attachment method can be considered in which a plug that is provided with a catch is pressed into the fluid port under the assumption that the plug will not be removed therefrom. However, under these circumstances, such a method cannot meet the needs of a user who, for various reasons, wishes to remove the plug. In contrast, a construction can be considered in which the plug is fit into the inner periphery of the fluid port with some play so that the plug can be removed therefrom. However, in this construction, the coupling force (frictional force) of a fluid sealing portion (for example, an O-ring), which is provided between the plug and the socket when the fluid path is formed, is strong, and there is a concern that the plug may be pulled out from the fluid port along with the socket.